1. Field of the Invention
The present invention relates to a toner, a development agent, and an image forming apparatus that uses the toner and development agent.
2. Description of the Related Art
In electrophotography, electrostatic images (latent images) are formed on an image bearing member (typically photoreceptor) and developed with toner into toner images. The toner image is transferred to a recording medium, typically paper, and thereafter fixed thereon using heat, pressure, or both.
In an image forming apparatus employing a heating fixing system, since a large amount of energy is required in the fixing process of fusing the toner on the recording medium, fixing the toner at a low temperature is desirable in terms of saving energy.
To improve the low-temperature fixability of the toner, it is necessary to control the thermal characteristics of the binder resin that accounts for a large proportion of the toner material.
For example, JP-2010-077419-A describes a toner having a crystalline resin accounting for most of the binder resin to provide a good combination of low-temperature fixability and high-temperature stability by controlling the composition and the thermal characteristics of the crystalline resin.
In addition, JP-2009-014926-A describes using a toner containing two kinds of crystalline resins (preferably crystalline polyester resins) having different molecular weights as the binder resins under a particular fixing condition to improve the low-temperature fixability and prevent fixed images from cracking.
In addition, JP-2010-151996-A describes a toner containing two kinds of crystalline resins having different storage elastic moduli at 160° C. as the binder resin to provide a good combination of low-temperature fixability and the high-pressure preservability. Moreover, JP-3287733-B (JP-H8-50368) describes using an ester wax having ester compounds having the same total number of carbon atoms in an amount of 50% by weight to 95% by weight as a releasing agent, so that the releasing agent drastically melts at a particular temperature (melting point) to provide good transparency for a transparent sheet while improving the low-temperature fixability, the hot offset resistance, and the high-temperature stability.
The present inventors have found that, in toner having a crystalline resin as the binder resin, as the ratio of the crystalline resins increases from 30% by weight to 40% by weight, 50% by weight, and so on, low-temperature fixability improves, particularly when the crystalline resin is the major component of the binder resin. However, this also invites peeling-off of the image during the low-temperature fixing process and occurrence of slight cold offset, which are large impediments to further improvement of low-temperature fixing.
In addition, as low-temperature fixability improves, it is possible to lower the surface temperature of a heating medium (such as a roller or a belt) during fixing, thereby decreasing the power consumption of the image forming apparatus. However, as the surface temperature of the heating medium decreases, the temperature fluctuates greatly particularly in the case of continuous printing, which causes problems such as production of defective images and winding of the recording medium around the heating medium. This tendency is particularly pronounced when using a releasing agent having a low melting point and demonstrating a releasing effect by drastic fusion at a particular temperature.
In addition, with toner having a binder resin high in crystalline resin, the high-temperature stability of the toner mainly depends on the melting point of the crystalline resin. However, the melting point of the crystalline resin drops significantly when the releasing agent contains a component that melts at a low temperature, thereby degrading the high-temperature stability significantly. Furthermore, the low-melting-temperature component of the releasing agent tends to be volatile, which creates a problem of contamination of the interior of the machine.